1. Field of the Invention
The present invention relates generally to the field of orthodontic devices and methods for maintaining an orthodontic archwire relative to a tooth. More specifically, the present invention discloses an orthodontic bracket with a removable clip that can be inserted into the bracket slot of the bracket along the axis of an archwire to secure the archwire to the bracket.
2. Statement of the Problem
In the field of orthodontics and orthodontic armamentarium, the orthodontic bracket is a central component of current, orthodontic practice. Orthodontic brackets were first developed by Dr. Edward Hartley Angle in the late 1800's and in spite of significant improvements in design, materials and manufacturing processes that have occurred since Dr. Angle's time, the biomechanical functioning of orthodontic brackets remains essentially unchanged.
The primary functional feature of conventional orthodontic brackets is the archwire slot. The archwire slot is a generally horizontally oriented, outwardly opening, rectangular-in-cross-section trough formed in the structure of a bracket intended to accept a separate, round, square or correspondingly rectangular-shaped archwire. A refinement of the orthodontic bracket developed by Dr. Angle is known as the “edgewise”-type bracket. The term “edgewise” is a descriptive term referring to the rectangular inter-fit of the archwire slot and the rectangular archwires typically employed for edgewise orthodontic therapy. The rectangular inter-fit of the archwire in the bracket's slot enables full conveyance of corrective energy stored in a deflected archwire to be transmitted to the tooth, the root and into the bony support structure of a patient's jaws.
The archwire slot of conventional orthodontic brackets consists of an archwire slot floor and two archwire slot walls. The walls are parallel to each other and are in turn generally parallel to the occlusal plane. The floor of the slot is oriented perpendicular to the walls thus forming two 90° corners extending along the floor. Such an archwire slot is considered as being an “open” slot because an archwire can drop into it from the labial or buccal directions due to the slot having no fourth side.
Within the field of orthodontics, dimensional standards have been established for the dimensions of archwire slots. For example, the standard dimensions of 0.018 and 0.022 inches relate the slot width, plus an allowance for manufacturing tolerances. These values are known as “slot size”. The depth of the slot may be 0.025 in. for a slot that is 0.018 in. wide, and 0.028 in. for a slot that is 0.022 in. wide. Brackets with the standard 0.018×0.025 in. and 0.022×0.028 in. archwire slot dimensions are available to orthodontists from many commercial sources.
Even though Dr. Angle's bracket design has become the standard and is utilized widely, edgewise brackets still have limitations and shortcomings in use. For example, at a later stage of treatment orthodontists will typically attempt to insert what is known as a full-size or finishing archwire into the archwire slots of a patient's brackets. Such archwires are generally very stiff, having a tensile strength of up to 310 KSI UTS and a modulus of elasticity approaching 30,000,000. The term “full size” relates to an archwire that is manufactured to rectangular dimensions that fully fill a bracket's archwire slot thus taking full advantage of the edgewise philosophy. In such a relationship, the walls and floor of the archwire slot will be in intimate, coplanar contact with the outer surfaces of such an archwire. It must be understood that the stage of treatment where an orthodontist would first attempt to insert a full-size finishing archwire coincides with the patient's teeth having been only partially repositioned toward their ideal finished positions. The patient's teeth at such a stage lack final aesthetic and gnathologic positioning required for a stable occlusion and a good finished result. Because of this, the various bracket archwire slots will fall somewhat out of alignment relative to each other just as the teeth they are attached to are. Due to the difficulty associated with attempting to insert a very stiff and tightly-fitting archwire into various unaligned archwire slots, an orthodontist must often times use instruments known as torqueing wrenches to distort the archwire locally at each bracket/archwire interface. The wrenches are used to bend and orient the archwire so that it can drop into its corresponding bracket's archwire slot. For the next adjacent bracket the archwire must again be distorted to conform to the orientation of its archwire slot. Such distortion then is biased against the previous bracket's orientation and will in turn be biased relative to the subsequent bracket's orientation, and this difficult and time consuming process must be repeated all around the patient's arch. As can be appreciated, wrestling a finishing archwire into typically ten archwire slots around the patients upper or lower dental arch is time-consuming for the orthodontist and can be uncomfortable for the patient.
Throughout the foregoing, it should be appreciated that orthodontic treatment is initiated with archwires exhibiting a low spring rate and high deflection, and sequentially superseded with archwires that exhibit progressively higher spring rates at lower deflections. Over the course of treatment the steps of removing and then replacing a series of sequential archwires consumes a significant portion of the total time an orthodontist and staff can devote to a patient's care.
In all cases, once archwires are positioned into the series of archwire slots, the archwire must be then retained in each of the slots. Standard orthodontic brackets have features known as ligation wings or tie wings that are intended to inter-work with a separate ligature device thus creating a means with which to hold archwires fully seated and in place in the brackets.
Ligatures can be formed from urethane elastomers using the injection molding process. Such elastomeric ligatures are configured in the shape of tiny o-rings. Elastomeric ligatures are hooked over one pair of a conventional bracket's tie-wings and then pulled up and over the archwire and hooked over the opposite pair of tie wings. Orthodontic instruments are typically required to accomplish the step of ligation.
Stainless steel ligatures may also be used. Stainless steel ligatures are formed from fully annealed 0.009 inch through 0.012 inch diameter round wire. Steel ligatures are similarly tied around the tie wings of a conventional bracket and over the archwire thus retaining the archwire in its archwire slot. Once tied, the loose ends of the wire are twisted and the excess wire is cut off. The twisted section of the wire is then tucked under the tie wings so as to be out of the way to avoid laceration of the soft tissues of the tongue and cheeks. Similar to ligation using elastomeric ligatures, steel ligatures also require the use of several specialized dental instruments.
From the foregoing, it can be seen that the steps of installing, removing and replacing archwires (particularly full-size finishing archwires) are a time consuming and sometimes challenging task for an orthodontist and staff. The changing of archwires can also be a painful experience for the patient. The step of ligating archwires into each of the brackets is likewise a time-consuming aspect of orthodontic treatment that requires dedicated instruments and focused attention on a tooth-by-tooth basis.
In addition to the limitations of conventional brackets as described above, the standard configuration of conventional orthodontic brackets creates other problems. For example, occlusally-extending and gingivally-extending tie wings shield the facial surfaces of the teeth from tooth brushing and irrigation creating conditions that are ideal for the growth and protection of oral bacteria. The consistent presence of bacteria under the tie wings of a conventional bracket can lead to decalcification of the enamel adjacent to brackets. The presence of bacteria over time can deplete the oxygen bound up in the passivating surface of stainless steel leading to a potential for corrosion problems of the orthodontic hardware itself.
The spacing of the features of conventional brackets, particularly in an occlusal-gingival axis required to accommodate the tie wings and a central slot requires that a standard bracket be at least 3.2 mm in occlusal-gingival extent. This minimum requirement means that a conventional bracket cannot be less than a set minimum size and therefore conventional brackets are considered by some as unavoidably large. Large brackets can contribute to soft tissue irritation and patient discomfort, which can then impact a patient's attitude and loss of the important willingness of a patient to cooperate with his or her treatment. Large brackets can also contact teeth on the opposing arch which can cause damage and wear. Orthodontic patients are often self-conscious, and a “metal mouth” appearance associated with the large relative size of conventional orthodontic brackets can be another factor that does not foster a cooperative attitude by the patient.
Efforts have been made in the past to address these shortcomings and limitations associated with conventional edgewise orthodontic brackets. For example, U.S. Pat. No. 5,356,288 (Cohen) discloses a “primary bracket” with a horizontal slot for receiving an archwire, and a “secondary bracket” that attaches to the primary bracket to hold the archwire in place. Cohen discloses embodiments in which the secondary bracket slides axially into the slot in the primary bracket. However, only one surface of the archwire, at most, is engaged by the walls of the primary bracket. The other surfaces of the archwire are either engaged by the walls of the secondary bracket or remain unsupported. This approach has significant shortcomings in terms of strength and rigidity, and also tends to require a larger bracket assembly.
In particular, Cohen's secondary bracket must be oriented in axial alignment with the primary bracket for the two parts to slide together. Now, assume that a tooth is significantly intruded relative to an adjacent tooth. During a typical early stage of treatment, the archwire must zigzag in a significant bend after exiting the bracket on the first tooth to engage the bracket on the adjacent tooth. Since Cohen's secondary bracket constitutes essentially an upside-down three-sided arch slot, with a labial slot floor, and perpendicular to that, parallel occlusal and a gingival walls, the secondary bracket fully captures the archwire and restricts its true position to that of being axially aligned, and contained within the secondary bracket. The secondary bracket must, in turn, be held in precise alignment with the primary bracket even when the secondary bracket is only beginning to be inserted into the primary bracket of Cohen. In such an example, the distal end of the secondary bracket would inherently be located in very close proximity to the mesial edge of the bracket on the adjacent tooth while inserting Cohen's secondary bracket into the bracket on the first tooth. This can result in an impossible configuration where during the step of inserting Cohen's secondary bracket, the archwire is asked to make an immediate and abrupt bend as it exits the distal end of the secondary bracket. Assuming any space exists for the archwire to make such a dramatic bend, such a sharp bend would induce a permanent set in the archwire impairing its ability to deliver corrective forces between the two teeth. Further, the act of inserting Cohen's secondary bracket into the primary bracket could be a painful experience for the patient. Mechanically speaking, the only practical way to utilize Cohen's brackets would be to limit their use to a final finishing stage in which the teeth are closer to ideal alignment, combined with the step of manufacturing Cohen's brackets in extremely narrow mesial-distal widths. Utilizing Cohen's brackets would require an orthodontist to remove all of a patient's conventional brackets and replace them with Cohen's brackets for final finishing treatment. There is no cost or treatment benefit to justify such an unorthodox step, and further, Cohen's brackets have no features that would eliminate the positional errors unavoidably suffered in positioning any type of bracket on a tooth. Brackets that were manufactured sufficiently narrow in a mesial-distal extent to allow Cohen's secondary bracket to be inserted without destroying the archwire would then create excessive inter-bracket distance which would impair the required level of physiologically-effective corrective forces to be delivered to the teeth.
Solution to the Problem. The present invention addresses the shortcomings of the prior art by providing an orthodontic bracket with a removable clip that can be inserted into a bracket slot from the lateral edge of the bracket along the axis of the archwire to secure the archwire to the bracket. Two of the archwire surfaces are engaged by the clip and the remaining two archwire surfaces are engaged by the walls of the bracket slot. This approach allows the shapes of the clips to be tailored to the cross-sectional dimensions of each archwire over the course of treatment to simplify insertion of the archwire and clip into the bracket slot, and more securely hold the archwires in place.
There are additional advantages arising from having two archwire surfaces engaged by the clip and the remaining two archwire surfaces engaged by the bracket. This arrangement captures the archwire in one of the corners (i.e., occlusal or gingival) of the bracket slot adjacent to the base of the bracket. If the bracket slot and clip are symmetrical or when multiple, right/left-hand clips are use, the practitioner can select which slot corner to most advantageously position the archwire by flipping the orientation of a clip or using the correct configuration. This enables the practitioner to bias the archwire occlusally or gingivally for each individual tooth, to thereby facilitate needed intrusions or extrusions of teeth during orthodontic treatment.
In contrast to Cohen, the present invention employs a bracket slot that engages two sides of the archwire, and a clip that engages the other two sides. The clip provides only one wall that selectively contacts either the gingival or occlusal face of the archwire. In the example above with regard to Cohen, a practitioner would select one clip that engages the labial and occlusal side of the archwire. The archwire would then be completely free to naturally zigzag as required to elegantly curve into the lateral bracket. The archwire is free to naturally curve to the bracket on the adjacent tooth irrespective of whether the clip is inserted only partially into the first bracket or completely locked in place.
The present invention also eliminates the need for tie wings and ligatures to hold the archwire in place in the bracket slot. This saves time and effort on the part of the orthodontist, and reduces patient discomfort. The absence of tie wings also reduces the visual impact of the bracket assembly, reduces patient discomfort, and eliminates potential places to harbor bacteria.